Diene polymerization, special case

The classification above is not exhaustive. Thus, the polymerization of a doubly-unsaturated monomer may fall within Class (i) if the double bonds are similar and so remote from each other that the reaction of one do not affect the reactivity of the other if the double bonds differ greatly in reactivity it may be a good approximation to regard it as within Class (ii), but if, as in the case of butadiene, reaction of one double bond profoundly affects the reactivity of the other, the polymerization requires special treatment. For this reason branching in diene polymerization is excluded from this review. 

The polymerization of cyclopentadiene represents only one type of monomer which can be employed in a Diels-Alder polymerization. In theory, a polymerization reaction should be successful if a monomer which contained both a diene portion and a dienophilic portion were subjected to polymerization conditions. The polymerization of cyclopentadiene represents a special case of this reaction type. Another type... 

Monomer A is polymerized in the presence of polymer B during in situ polymerization. In the simplest case, a non-cross-linking polymer is dissolved in a non-cross-linkable monomer and the monomer is then polymerized. In the most commercially interesting case, the polymer is a cross-linkable diene, whereas the monomer polymerizes to a thermoplast. In the special case of an interpenetrating network, a polymer network B is swollen in a cross-linkable monomer A, which then, in the ideal case, polymerizes to an independent polymer network A. 

Interpenetrating Polymer Networks (IPN). Polymerization of vinyl and diene monomers over an already formed molecule held in a pol5uner particle represents a special case of copoljnnerization. The interpenetrating polymer networks (qv) thus formed overcome many of the miscibility and other problems associated with physical blends of individual copolymers and leads to new compositions that are useful for coatings, adhesives, and caulks (14). Polychloroprene IPNs have been made by co-curing copolymers of l-chloro-l,3-butadiene [627-22-5], The 1-chloro-l,3-butadiene comonomer polymerizes in a fashion to increase the allylic chloride concentration in the copolymer backbone. The butadiene copolymer with l-chloro-l,3-butadiene (29) and octyl acrylate copolymer (30) improved the low temperature brittleness, oil resistance, and heat resistance of polychloroprene. 

As a special case, polyvinyl alcohol is not obtained by the polymerization of ethylene alcohol, because ethylene alcohol has an unstable enol structure that can easily form aldehyde by isomerism therefore, vinyl alcohol is only a hypothetical monomer of polyCvinyl alcohol). For the majority of polymers prepared by means of a double bond addition reaction of alkene and diene monomers, this nomenclature method is simple, intuitive, and widely used. 

A very special case among optically active dienes is given by chiral allenes. Polymerization of (-)-(R)-2,3-pentadiene by organometallic transition metal derivatives [59] gives an optically active crystalline polymer to which the structure reported in Table XVI has been assigned. In fact that structure is the only linear structure not possessing symmetry planes or mirror glide planes. 

Polymerization of dienes is a special case of the pol5mierization of unsaturated compounds and its course depends on the structure of diene used. 

Block copolymers represent a special class of polymer blends characterized by covalent bonding between the individual molecules comprising the blocks. The molecular structure (monodisperse molecular weights) achieved with anionic polymerization has allowed for styrene-diene and diene-diene AB and ABA block copolymers, offering well-defined morphologies. The phase separation morphology and properties of block copolymers have been well-covered in many references [656-660] and wiU not be detailed here. Blends of block copolymers with their homopolymer constituents as well as in other polymer blends will be discussed. Cases where minor amounts of block copolymers are included in polymer blends as compatibihzers have been noted in Section 3.7. 

---